The use of electronic article surveillance (EAS) systems for article theft detection has been widely adopted by retailers and other entities (e.g., libraries). In the retail context, these systems include special tags that are activated and affixed to articles for which theft detection is desired, along with tag detectors having transmit and receive antennas that typically are positioned at exits of a retail store. When an article is purchased, a store clerk deactivates or removes the tag at the point-of-sale (e.g., a cash register area), and the article may be carried past the tag detector without triggering an alarm. However, when an active tag (i.e., a tag that has not been deactivated) is carried past a tag detector, and the tag detector successfully detects the active tag, the EAS system generates an audible alarm to alert store personnel to a potential theft of an article to which the tag is attached.
Several types of EAS systems are prevalently used. For example, an acousto-magnetic EAS system includes a detector with a transmitter configured to emit periodic activation pulses at a given frequency (e.g., about 50-90 pulses at 58 kilohertz (kHz)) during an activation phase, and magnetic tags that emit oscillating signals in response to encountering activation pulses of sufficient power. Essentially, the activation pulses energize the tag during the activation phase, and the tag continues to emit the oscillating signals even after the activation signal is discontinued. When the tag is within range of the detector and the detector is in a detection phase, the oscillating signal produced by the tag induces an AC voltage in a receive antenna of the detector. When the induced signal meets predefined detection parameters (e.g., the detected signal has a frequency of 58 kHz and is time-synchronized with the transmitter), the system may produce an audible alarm.
In contrast, each tag of a swept radio frequency (RF) EAS system includes circuitry with a resonance peak within a certain frequency range (e.g., from 1.75 to 9.5 megahertz (MHz), with 8.2 MHz being most popular). A transmitter of the system's detector transmits a relatively high-powered signal that sweeps around the pre-defined resonant frequency, and the tag responds by emitting a signal that may be detected by a wideband receiver of the detector when the tag is within a detection zone (e.g., an RF range of the detector). By detecting a phase difference between the transmitted and received signals, the receiver recognizes the presence of the tag within the detection zone, and the system produces an audible alarm.
Conventional EAS systems have been successful at deterring and detecting article theft. However, current systems suffer from some significant drawbacks. For example, a typical EAS detector includes a first pedestal to house the detector's transmit antenna, and a second pedestal to house the detector's receive antenna. Tag detection is possible when an EAS tag is carried between the transmit and receive pedestals. Accordingly, the transmit and receive pedestals are placed in proximity to a portal (e.g., a retail store exit) at a distance from each other that is governed by the signal characteristics of the detector. Current regulatory restrictions on a detector's transmitted signal characteristics, along with practical size limitations for EAS tags, mandate a relatively small distance between a detector's transmit and receive antennas (i.e., the distance between the transmit pedestal and the receive pedestal). Accordingly, when a portal is wider than the mandated distance, multiple pedestal pairs are needed in order to span the entire extent of the portal. The pedestal portions of current EAS systems are relatively expensive, and the necessity for multiple pedestal pairs to span a relatively wide portal increases the cost to the retailer of adopting such an EAS system. Additionally, the installation of multiple pedestal pairs may compromise the storefront aesthetics, and the pedestals may impede customer traffic at the front of the store. Accordingly, a retailer may decide not to purchase an EAS system when the system cost exceeds the perceived, potential benefit of theft deterrence/detection and/or when the retailer decides that the pedestals unacceptably compromise the storefront aesthetics or traffic flow.
An additional drawback to conventional EAS systems is that regulatory restrictions on EAS systems' transmit signal power result in EAS systems in which an EAS tag is detectable only when the EAS tag is located a relatively short distance from a pedestal pair. Typically, EAS tag detection is possible only when the EAS tag is very close to the pedestals and the store exit, and an individual carrying an active EAS tag may have exited the store before the EAS system alarm sounds, and store or security personnel are alerted. Accordingly, conventional EAS system operations often leave insufficient time or opportunity for store personnel to respond to a tag detection alarm (e.g., by apprehending an individual that is leaving a store with an active EAS tag).
In addition, conventional EAS systems are relatively inefficient with respect to power consumption. For example, as long as an EAS system is on (e.g., during a retail store's hours of operation), a conventional EAS detector continues to emit activation pulses (in the case of an acousto-magnetic EAS system) or to produce swept-RF signals (in the case of a swept RF EAS system). Accordingly, the EAS detector continuously consumes power while the system is on, regardless of whether or not an article theft potentially is occurring. Accordingly, what are needed are EAS systems and methods of their operation that overcome such drawbacks of conventional EAS systems.